Urea Dosing System with Thermal Protection and Pulse Control
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Solution Overview
Problem
Current urea injection systems face issues such as overheating, plugging, and non-uniform spray distribution due to premature air mixing and exposure to elevated temperatures, leading to inefficient NOx reduction in exhaust gas streams.
Innovation Solution
A system using a pressurized urea solution and compressed air, conveyed through concentric tubes with a mixing chamber and pulse-width-modulated flow control, providing a controlled air-assisted spray and thermally protective air flow to prevent premature mixing and plugging, ensuring uniform distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the urea injection valve is directly mounted on the exhaust gas conducting surface, then the injection is simple and direct, but the valve overheats and becomes prone to plugging
Solution Approach 1:
A thermally protective flow of air acts as an intermediary between the hot exhaust gas and the urea solution supply tube, preventing direct thermal contact and overheating of the injection valve while maintaining reliable operation
Solution Approach 2:
The system separates the urea solution supply path from the hot exhaust gas path by using concentric tubes, with the inner tube carrying the solution and the outer tube providing thermal protection, thus segmenting the thermal zones
2Quantity of substance
If multiple holes are provided in the atomizer tip, then spray distribution should be improved, but non-uniform spray flow occurs especially at low dosing rates
Solution Approach 1:
Compressed air is introduced through the outer tube to create a co-flowing air stream that entrains and distributes the urea solution uniformly across all holes in the atomizer tip, ensuring consistent spray patterns even at low dosing rates through pneumatic assistance
Solution Approach 2:
The system changes the physical parameters of the spray by introducing pressurized air that modifies the flow velocity, pressure distribution, and atomization characteristics, transforming the spray from non-uniform to uniform across all holes
3Device complexity
If the urea solution is exposed to elevated temperature environment, then the injection process is simplified, but partial evaporation of water occurs in the supply tube causing plugging
Solution Approach 1:
A continuous flow of air serves as a thermal barrier and protective intermediary between the hot exhaust environment and the urea solution in the supply tube, preventing water evaporation and plugging while maintaining process simplicity
Solution Approach 2:
The system creates a protective air environment around the urea solution supply tube that isolates the solution from the hot exhaust gases, effectively creating a thermal isolation zone that prevents evaporation and maintains solution integrity
4Stability of the object's composition
If the mixing chamber volume is large, then mixing is more thorough, but the system complexity and size increase
Solution Approach 1:
The system uses pulsed injection of urea solution into the exhaust stream, creating periodic mixing events that achieve thorough mixing in a compact volume by leveraging the dynamic motion and turbulence of repeated injection cycles rather than requiring a large static mixing chamber
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system achieves a consistent, uniform, and thermally stable urea-water spray into the exhaust gas stream, reducing plugging and improving atomization quality, thereby enhancing NOx reduction efficiency and maintaining the urea solution's integrity.
Implementation Method 1
A first elongated tube in fluid communication with the source of the pressurized solution of urea and water has a check valve disposed in a distal end
Implementation Method 2
A second elongated tube that is in fluid communication with the source of the compressed air is disposed in concentrically spaced circumscribing relationship around the first elongated tube
Implementation Method 3
The distal end of the second elongated tube is adapted to be positioned in an exhaust conduit
Implementation Method 4
each of which are adapted to provide a controlled air-assisted spray of the solution of urea and water into the exhaust gas
Data Source
AI summary
An aqueous urea dosing system has a first tube through which the urea solution is conveyed to a small mixing chamber. Compressed air is continuously conveyed through an annular space between the outer surface of the first tube and the inner surface of a second tube which has a distal end that extends beyond a distal end of the first tube. The mixing chamber is positioned between the respective distal ends of the first and second tubes. The urea solution is discharged into the small mixing chamber, and subsequently immediately into an exhaust gas, in a series of discreet pulses, the width and period of which are controlled by a pulse-width-modulated flow control valve spaced from the exhaust gas.